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I've owned several buildings. The one I now have at my home property is a
stand alone 30'x40'. It has Fiberglass batts in the walls, foam & foil panels
for ceiling. I also have full drywall on all sides.

It is more than sufficient. I simply can't see spending that extra $3,500 on
more insulating. I would think that money would be much better served
somewhere else.

When I built my shop I did all spray foam in the walls and batts with blown in the ceiling (R-48) equivalent. All 3 garage doors are 2" thick insulated as well. It was the best money I ever spent. I leave the thermostat on 50* all winter and turn it up when I'm out there working. I have a radiant tube for heat, costs me $25/mo.

The biggest advantage of spray foam is that it creates a complete barrier......you get zero air leaks. Batting or blown in will always have air leaks around outlets, against studs, corners etc.

When I built my shop I did all spray foam in the walls and batts with blown in the ceiling (R-48) equivalent. All 3 garage doors are 2" thick insulated as well. It was the best money I ever spent. I leave the thermostat on 50* all winter and turn it up when I'm out there working. I have a radiant tube for heat, costs me $25/mo.

The biggest advantage of spray foam is that it creates a complete barrier......you get zero air leaks. Batting or blown in will always have air leaks around outlets, against studs, corners etc.

--Joe

That is the best part about the foam. You can seal all of the outlets and suspect problem areas with caulk/spray foam etc and save a ton of cash. Your heating bill is pretty impressively low though.

Thanks guys - really good ideas. I'll ask about a thin layer of foam just to act as a vapor barrier.

For the garage, walls will be R-19 batts, with insulated doors. I am thinking I'll end up with the R-30 batts in the garage ceiling (workshop floor) due to the cost, but will ask about foaming as a vapor barrier. The entire garage - ceiling and all - will be drywalled.

Workshop (2nd story), I will figure out...at this point, it's going to be studs. I'll do blown-in in the attic space there eventually, and I am undecided as to what I'll do on the walls. I plan on installing a DIY (MrCool) mini-split up there. I didn't even think of a vapor barrier - just reached out to the builder to see what his plan is for that. Makes sense that I need something.

One thing not to forget about though, especially in the winter time with a garage that has constant cars covered in snow and wet coming in for the night, you can seal a building too tight too. I'd vapor barrier just the ceiling between the garage and work shop area, and use normal fiberglass with paper backing in the walls, it'll allow the building to breathe and dry out, instead of holding all that moisture and humidity. It'll still hold plenty of heat that way.

In my eyes the only downside of foam is if you have to do any electrical or plumbing work later, but chances are you could add/route whatever you needed in the walls instead. The vapor barrier seems like a good reason to spend the $$$ in this case. Also, let me know how the mini-split setup turns out, i want to put one in my 2 car garage myself.

when i just built my house i had them not insulate the garage and i'd do it myself. Bad choice. totally wish i would have just had them do it as i already had them do all the electrical and everything in it except the heating system. i did ti with fiberglass and they would have spray foamed it. for roughly 1.5 times the amount. but it would have been well worth it to me. the foam is way better.